Solo 401(k) calculator

The $24,500 employee limit counts across every 401(k), 403(b), SIMPLE and SARSEP you are in, so what you defer at a job leaves less for your own plan. A 457(b) has a limit of its own. The employer side is separate: your employer’s match doesn’t touch your Solo 401(k)’s $72,000, unless you own more than half of that employer.

Social Security’s 12.4% stops at $184,500 of combined wages and self-employment earnings for 2026, and a job’s wages count first. With a large salary, the business pays only Medicare’s 2.9%, so half the self-employment tax is smaller and more of the profit counts as earned income. On $60,000 of profit beside a $200,000 salary with $15,000 deferred at the job, the employer part is $11,839 rather than the $11,152 a calculator ignoring the job would show.

Above $200,000 ($250,000 filing jointly) an Additional Medicare Tax applies. It isn’t part of the half of self-employment tax that comes off, so it doesn’t change the limits.

What counts is your age on December 31. The catch-up starts the year you turn 50; the larger one covers the years you turn 60, 61, 62 and 63, and at 64 it goes back to $8,000. There is no upper age limit for putting money in. Catch-ups are per person too, so one made at a job uses up the same allowance.

Everything you put in has to come out of what the business earned. On a small profit the employee part fills first, and the employer part can shrink to little or nothing.

Roth contributions count toward the same limits but come off nothing this year. If an S corporation paid you more than $150,000 in wages last year, your catch-up there has to go in as Roth. A sole proprietor has no wages from the business, so the rule doesn’t apply.

Open the plan and choose your employee amount by December 31; the money can go in up to your filing deadline. With no employees you can still open a plan until April 15, 2027 for 2026. The employer part can go in until your deadline with extensions.